OFFSET
1,1
LINKS
K. D. Bajpai, Table of n, a(n) for n = 1..4000
EXAMPLE
a(1) = 23 is Sophie Germain prime because 2*23 + 1 = 47 is prime. Also, 23 + 2 = 25 = 5*5; 23 - 2 = 21 = 7*3; are both semiprime.
a(2) = 53 is Sophie Germain prime because 2*53 + 1 = 107 is prime. Also, 53 + 2 = 55 = 11*5; 23 - 2 = 51 = 17*3; are both semiprime.
MATHEMATICA
Select[Select[Prime[Range[10000]], PrimeQ[2 # + 1] &], PrimeOmega[# - 2] == 2 && PrimeOmega[# + 2] == 2 &]
Select[Prime[Range[3000]], PrimeQ[2#+1]&&PrimeOmega[#+{2, -2}]=={2, 2}&] (* Harvey P. Dale, Dec 16 2017 *)
PROG
(PARI) is(n) = ispseudoprime(n) && ispseudoprime(2*n+1) && bigomega(n+2)==2 && bigomega(n-2)==2 \\ Felix Fröhlich, Nov 07 2016
CROSSREFS
KEYWORD
nonn
AUTHOR
K. D. Bajpai, Nov 07 2016
STATUS
approved